The reaction of 1-nitroso-2-naphthol with tyramine and tyrosine in the presence of nitric acid has been reported by Udenfriend et al., J. Biol. Chem. 1952, 196, pp.227-233. Specifically, it is disclosed:
"TYROSINE DERIVATIVE--To 200 mg. of 1-nitroso-2-naphthol dissolved in 150 ml. of ethanol were added 80 mg. of L-tyrosine dissolved in 300 ml. of 1M nitric acid. The mixture was heated at 55.degree. for 2 hours, cooled, and extracted four times with 500 ml. portions of ethylene dichloride to remove excess nitrosonaphthol. The nitrosonaphthol derivative was then extracted into 250 ml. of n-butanol, which was washed twice with equal volumes of water to remove dissolved acid. 1 liter of n-heptane was added to the n-butanol and the mixture was extracted with 200 ml. of water. Orange crystals appeared in the aqueous layer.
These were collected on a sintered glass filter and washed with water. The moist crystals were readily soluble in water. The absorption spectrum was qualitatively the same as that of the isolated nitrosonaphthol tyramine derivative (FIG. 1). When dried in vacuo, the material was no longer easily soluble in water and displayed a changed absorption spectrum, indicating that a chemical change had occurred."
The reaction of 1-nitroso-2-naphthol with tyramine or tyrosine was used for quantitative analysis of either tyramine or tyrosine; however, as set forth by Udenfriend et al.: "The method does not distinguish between tyrosine or tyramine." A product was produced by the reaction, usually red to yellow, which related to the concentration of tyrosine or tyramine added, but the reaction product was not identified. The quantitative analysis of materials known or suspected to contain tyrosine or tyramine were reacted with 1-nitro-2-naphthol in the same manner as the controlled reaction and the color intensity measured by a spectrophotometer. The concentration of tyrosine or tyramine was determined by comparing the measured reading from the spectrophotometer to a calibrated chart having the color intensity for known concentrations.